Inflammation is the complex biological response of tissues to harmful stimuli, such as pathogens, damaged cells, or irritants, as well as to mechanical trauma, toxins, and neoplasia. Inflammation occurs as a defensive response to invasion of the host by foreign material and is classified as either acute or chronic. Acute inflammation is the initial response of the body to harmful stimuli and is achieved by the increased movement of plasma and leukocytes from the blood into the injured tissues. A cascade of biochemical events propagates and matures the inflammatory response, involving the local vascular system, the immune system, and various cells within the injured tissue. Chronic (prolonged) inflammation leads to a progressive shift in the type of cells that are present at the site of inflammation and is characterized by simultaneous destruction and healing of the tissue from the inflammatory process.
Excessive inflammation or prolongation of the inflammatory process may lead to local tissue damage, to post-infectious syndromes such as in fibrotic lesions and to rheumatic diseases such as systemic lupus erythematosus and rheumatoid arthritis, or even to inflammatory response-induced diseases as diverse as diabetes, arteriosclerosis, cataracts, reperfusion injury, and cancer.